Clamp for gluing felt on piano hammers



March 2, 1954 s. E. ZACK 2,670,769

CLAMP FOR GLUING FELT ON PIANO HAMMERS 4 Sheets-Sheet 1 Filed April 28, 1951 5/- 52 I, I I I l I [I I I Q K 36 4a a4//4.2/l 046 34 46 as INVENTOR Samuel. E ZE1EK BYMWWMI ATTORNEYS March 2, 1954 s. E. ZACK CLAMP FOR GLUING FELT ON PIANO HAMMERS 4 Sheets-Sheet 2 Filed April 28, 1951 INVENTOR v Samuel E-ZEL1:K

ATTORNEYS S. E. ZACK CLAMP FOR GLUING FELT ON PIANO HAMMERS March 2, 1954 4 Sheets-Sheet 3 Filed April 28, 1951 w! #w MMM A 8 m m 3 8 Wm mm m mmj u cm M 3w 3 v B i i E i T H i h E Q 6 Q; I E WK March 2, 19.54 s, ZACK 2,670,769

CLAMP FOR GLUING FELT ON'PIANO HAMMERS Filed April 28, 1951 4 Sheets-Sheet 4 iNVENT-OR Samuel E ZEL|:K

BY I I ATTORNEYS Patented Mar. 2, 1954 UNITED STATES TNT OFFICE CLAMP FOR GLUING FELT ON PIANO HAMMERS ration of Illinois Application April 28, 1951, Serial No. 223,495

1 Claim.

The present invention relates, generally, to improvements in apparatus for making sets of piano hammers, and it has particular relation to new and improved apparatus for securing the felts to hammer moldings.

For many years, sets of piano hammers have been made in accordance with conventional procedure, using known standard equipment. First, a hammer molding, previously cut into the wooden pieces for individual hammers, is inserted in a retainer clamp. Each set of wooden pieces for a hammer molding ordinarily comes in an individual package which may be folded three ways to shorten its length. The separate pieces are packaged in the order in which they are cut from properly shaped pieces of wood molding, and th1s arrangement or order is preserved when the pieces are clamped together in the retainer clamp. The retainer clamp is then inserted in a press and a felt is laid over the mold in the bed of the press. Depending upon the particular type of piano hammers being made, the hammer molding may be first provided with an under-felt and thereafter with a top-felt, or only a single felt may be applied to the hammer molding. In all cases, however, each felt is applied in the same general manner, with the press being provided with the proper molds for the particular type of felt being applied.

A plurality of mold clamps are provided for use in conjunction with the press, each clamp including a base plate, a mold or caul, and clampin plates slidable transversely of the base plate. The base plat is provided with a longitudinally extending recess within which the mold or caul is received, the clamping plates being mounted on the base plate for transverse movement toward and away from the mold. Means, such as bolts, are provided for holding and locking the clamping plates to the base plate.

A mold clamp is properly centered in the press so that the hammer molding positioned in the retainer clamp may be moved vertically downward into the mold or caul. A felt is properly centered over the mold, a coat of glue is applied to the opposite sides of the hammer molding in the press, and then the press is operated to cause the hammer molding to force the felt into the mold. Thereafter, the clamping plates are moved inwardly toward the hammer molding to force the edges of the felt against the opposite sides of the hammer molding. The clamping plates are then looked to the base plate in this position and the pressure applied to the hammer molding through the retainer clamp is maintained 2 for a certain length of time, after which the retainer clamp is released and raised so that the mold clamp may be removed from the bed of the press and stored in a convenient location until the lue has dried. The mold clamp is then opened and the hammer'molding, with the felt secured thereto, is removed from the mold. If this felt is the under-felt, then the hammer molding is put into a press, provided with the proper molds, and a top-felt is applied in the same manner as the under-felt.

The present invention is directed to the mold clamp, and particularly, to the base plate and the mold received therein. The primary object of the invention is to improve the hammer molding clamp to provide for increased efficiency in manufacture and increased production rates.

In the mold clamps presently used in the industry, the mold or caul, of hard maple wood, is tapered lengthwise and is driven tightly into a longitudinally tapered groove or recess at the center of the upper face of the base plate of the clamp. The recess is open at both ends for the insertion and removal of the caul. The caul, when driven in, exerts a wedging action to provide a firm mounting for the caul in the base plate. This construction has been considered necessary, since the hammer molding is forced. into the mold at high pressure to compact the felt into a firm bond between the hammer molding and felt. Because of this the mold must be firmly supported by the base plate. The mold is removable from the base plate for the reason that certain portions of the mold cavity are particylindrical, and the hammer molding and the felt secured thereto cannot be removed from the mold except by removing the mold from the base plate and then removing the hammer molding and its associated felt from the mold after the pressure on the mold has been released.

When the mold or caul is driven into the recess or groove in the base plate, it exerts a wedging action which pulls the base plate slightly downwardly at its sides and upwardly at its center. When the felt covered hammer molding is forced into the caul under high pressure, the central or caul area of the base plate is forced downwardly so as to remove the bow or camber temporarily, that is, during the pressing operation. After the clamping plates have been moved and locked into tight contact with the shoulders of the hammer molding and the press plunger is raised, the downward pressure on the caul in the central area of the base plate is relieved. The felt, as compressed, is under high pressur and exerts great expansive force on the caul and the clamping plates, tending to spread the caul laterally and to force the clamping plates apart. This force, supplemented by the bowing of the base plate by the caul, results in again bowing the base plate and moving the clamping plates a slight distance away from the sides of the molding. Such movement of the clamping plates releases the pressure on the felt and the corresponding areas of the hammer molding. The spreading of the caul, the bowing of the base plate, and the moving of the clamping plates, causes relief of pressure over various areas of the hammer molding, and the felt is not properly glued to the molding at those areas. Improper gluing results in imperfect hammers, which must be either repaired or rejected, at a substantial increase in cost of production, since soft or improperly glued felts cannot be used to give satisfactory and proper tonal qualities in a piano.

In addition to the foregoing defects, the clamps presently used suifer from the fact that the base plate is subjected to lengthwise twisting. In certaln constructions, the base plate is formed of a solid casting and in these cases, the lengthwise or longitudinal twisting is sufliciently resisted by the materials of the base plate. In other constructions, however, the base plate has recessed portions to lighten the weight of the base plate and a central beam or rib is provided within which the caul receivin groove is formed. This central beam has the same taper exteriorly as does the groove. When the caul is driven into the groove, the base plate tends to bow most at the end corresponding to the thinner end of the beam, which is the thinner end of the groove, so that the transverse bowing is accompanied by the longitudinal twisting of the base plate, which contributes to the lack of, or defective, gluing, particularly at the smaller hammer area of the mold- Due to the fact that the present day mold clamps are subject to the foregoing defects, it

has been found necessary to counteract the bowing of the base plate and the movement of the clamping plates by leaving the clamps in the press under plunger pressure for a minimum of fifteen minutes to reduce the number of unglued or imperfectly glued areas. Accordingly, the maximum output of the press is limited to four moldings per hour.

An object of the present invention is to provide an improved molding clamp that does not suffer the defects of present day clamps and provides increased efiiciency and rate of production of felted piano hammers.

Another object of the invention is to provide an improved mold clamp for securing felts to piano hammer moldings, which provides and includes reinforcements or reinforcing portions for preventing bowing and twisting of the base plate of the clamp.

A further object of the invention is to provide improved mold clamps having a reinforced base plate to prevent bowing and twisting, the provision of the novel reinforcements requiring variations and changes in methods of manufacture which heretofore have been regarded as essential to the formation of satisfactory felted piano hammers.

A further object of the invention is to obviate the necessity for wedging the caul or mold into the base plate of the clamp.

A still further object of the invention is the provision of a readily and economically manufactured mold clamp, which is light in weight, and can be easily placed on and removed from the bed of the press, and which can be readily and compactly stored with other mold clamps.

In accomplishing the various objects of the present invention, I provide an improved base plate havin a central longitudinal groove in its upper face, the groove being closed at its ends by walls or bridges of substantial height and thickness. The caul is inserted vertically into the groove and conforms in size and shape to the groove, into which it fits tightly, but without any pronounced wedging effect. The end walls or bridges at the ends of the grooves, prevent bowing of the base plate, and the lack of any wedging action by the caul also contributes to the prevention of bowing or twisting. Accordingly, there is no bowing of the base plate and no movement of the clamping plates when the press plunger is raised, the felt being effectively glued to the hammer molding for its full extent. Effective gluing eliminates the necessity for repair or rejection of certain hammers, materially reducing the cost of production. Furthermore,

since the pressure need not be maintained by the press plunger to prevent bowing, the press may be opened and the clamp, with the molding, removed as soon as the clampin plates have been closed and locked to the base plate, This enables an output of approximately thirty moldings per hour, which further materially reduces the cost of production of felted hammers for pianos.

Other objects and advantages of the present invention will become apparent from the follow.- ing detailed description of a preferred embodiment of my invention, wherein reference is made to the accompanying drawings, in which:

Figure 1 is a semi-diagrammatic view, in partial side elevation, of a press having the clamp .of the present invention positioned on the bed thereof;

Figure 2 is an end view, partly in elevation and partly in section, of the mold clamp of the present invention with the clamp locked about a hammer molding and the felts associated therewith, the view being taken at the narrow or treble end of the hammer molding;

Figure 3 is a top plan view of the clamp of the present invention with the mold or caul mounted in the base plate;

Figure 4 is a top plan view of the base plate of the clamp of the present invention with the caul mounted therein;

Figure 5 is a bottom plan view of the base plate of the clamp of the present invention;

Figure 6 is a cross sectional View, taken substantially on the line fi6 of Figure 3, with the clamp locked upon a hammer moldin the view being taken at the wide or bass end of the hammer molding;

Figure 7 is a cross sectional View of the base plate with the caul inserted therein, the view being taken on the line 'l'i of Figure 5; and

Figure 8 is a partial sectional view taken along the longitudinal axis of the base plate, on the. line 88 of Figure i.

In Figure 1, there is shown diagrammatically, a press It provided with a pair of upright guides i2. A plunger operated crosshead H8 is vertically reciprocable in the guides 12 and carries a retainer clamp is within which a hammer molding i8 is clamped. The press is provided-with a bed plate 20 open at both sides for the reception of a mold clamp 22. In the molding operation, the

mold clamp 22 is slid onto the bed plate 20 transversely of the press and is centered with respect to the crosshead l4, so that the hammer molding It may be moved into the mold cavity in the clamp 22.

The mold clamp 22 comprises a base plate 24, a pairof clamping plates 26 mounted on the base plate 24 for transverse movement with respect thereto, bolts 28 secured to the base 24 and extending through the clamping plates 26 for the reception of washers 30 and nuts 32 for detachably mounting the clamping plates 26 to the base plate 24.

The base plate 24 is cast of any suitable material .and may be formed either solid or with recesses, depending upon the strength of the material from which the plate is cast. The base plate is preferably cast from lightweight strong metal, such as magnesium, and is provided with a plurality of symmetrically disposed recesses 34 to lighten the weight of the base plate. The recesses 34 also serve to receive the bolts and nuts of another clamp when the clamps are stacked upon one another prior-to being used. The recesses 34 in the base plate define side walls 36, end walls 38 and a central longitudinal rib or beam 40. The side walls, the end walls and the central beam are of substantial thickness so as to resist any forces to which the base plate may be subjected. A longitudinal groove 42 is formed in the upper surface of the central rib or beam 40 for the reception of the caul or mold. End walls or bridges 44 are provided at either end of the groove 42 and the walls 44 constitute integral extensions of the end walls 38. The end walls 44 are of substantial section, at least to one inch, to prevent bowing or twisting of the base plate. The base plate is provided at regular intervals with integral transverse ribs 46 within which tapped holes 48 are formed for the reception of the bolts 38. The groove 42 may be either uniform or tapered as desired, and the central rib or beam 44 of the base plate maybe either uniform or tapered, as desired, the end walls 44 of the groove 42 cooperating with the side walls 36, end walls 38, and beam 40 to prevent bowing or twisting. However, to avoid undue stress, the groove 42 and rib 44 preferably are each uniform. The side walls of, the groove 42 are preferably provided with a vertical taper as shown in Figures 2, 6, and 7.

A mold or caul 54 is received within the groove 42 and is preferably formed of two elongate pieces i and 52, each defining half of the mold cavity. The mold or caul is preferably formed of hard wood, such as hard maple, and is preferably formed in two pieces, as shown,'to facilitate the ready detachment of the caul and the felted hammer after the molding operation. The caul may, however, be formed in a single piece, if desired. The caul is inserted vertically into the groove 42 and has a tight, but not a wedge fit in the groove 42. This particular construction differs from previously proposed arrangements, in which the caul was wedged into the groove horizontally, both the groove and the caul being tapered to facilitate the wedging action. Since the caul is not wedged into the groove, the twisting of the base plate is obviated to a substantial extent, but, as stated, the rib 4B is preferably of uniform thickness, the groove 42 is of uniform width and the caul 50 is of uniform width to prevent setting up of stresses in the base plate. The vertical taper of the walls of the groove serve merely to guide the caul properly into the groove and provide firm support for the caul. The cavity in the caul is tapered, as shown in Figures 3 and 4, to provide for the proper variation in size for the various hammers to provide the proper tonal qualities for the piano. At one end, the mold cavity is substantially tear-drop in shape, as shown in Figure 2, for the formation of the treble keys. The mold cavity at the opposite end is parti-cylindrical, as shown in Figure 6, for the formation of the felts at the bass end. The roove 42 and the central rib or beam 40 of the base plate 24 may be tapered or may be of uniform width, but the caul, in all cases, must be of the same configuration as the groove 42 so as to conformably fit within the groove 42 for firm support thereby, yet without wedging action. Whether the groove be tapered or uniform, the caul 54 i inserted vertically into the groove so as to be readily inserted and removed therefrom.

The clamping plates 26 may be cast in solidsection, but are preferably cast from a lightweight, strong metal, such as magnesium, and are provided with recesses 56 to lighten the clamps to facilitate their movement. Each clamping plate is approximately half as wide as the base plate and is somewhat shorter than the base plate. At equally spaced points throughout the length of the clamping plates, slots 58 are provided, which register with the tapped holes 48 in the base plate 24. The slots 58 are of a size and shape to loosely receive the bolts 28 so that the clamping plates may be moved transversely of the base plate within the limits defined by the length of the slots 58. The washers 30 engage the upper surface of the clamping plates 55 and are adapted to be tightened down on the clamping plates by means of nuts 32 tolock the clamping plates in a desired position with respect to the base plate 24. The inner longitudinal edge or face of each clamping plate is vertically tapered, as at 5B, for engagement with the opposite walls of the hammer molding l8 and the felts to be secured thereto. The vertical taper of the inner faces of the clamping plates varies throughout the length of the plates so as to coincide with the side walls of the mold cavity to properly form the felt or felts to be secured to the hammer molding.

In use, a molding clamp 22 is centered on the bed platettfl of the press iii, a felt is fitted over the mold cavity, a hammer molding I8 is positioned in the retainer clamp Hi, the opposite sides of the hammer molding are glued, the hammer molding and retainer clamp are moved down-- wardly by the press plunger to move the hammer molding into engagement with the felt and force the felt into the mold cavity, extreme pressure is applied to the hammer molding by the .press plunger to cause intimate engagement between the felt and the mold and between the felt and the hammer molding, the clamp plates are then moved inwardly, and in most presses, the inward movement of the clamping plates is effected by means of fingers or pressing members 65, see Figure 2, to cause the clamping plates to force the edges of the felt into intimate engagement with the opposite sides of the hammer molding, the nuts 32 are then tightened to lock the clamping plates in the felt engaging position. After the clamping plates have been locked in position, the hammer molding I8 is removed from the retainer clamp is and the press plunger is elevated to move the cross head I 4 upwardly and the pressing members 65 laterally away from the mold clamp 22, so that the mold clamp 22 may be r moved'from the. bed plate of the press and stored in some convenient location until the ue has dried. The described operation is performed in a proximately two minutes.:.and the press "I is then ready for the reception of another mold clamp: 22. for repetition of the operation. After sufficient time has been allowed for the glue to. dry, the nuts 32 are loosened so that the clamping plates 26 maybe moved. transversely with respect to the base plate 24 to release the hammer molding and the caul 5.0 from the base late 24. The. hammer molding and caul are readily removed from the. base plate 24 by exerting a lifting effortonthe upper portion of the hammer molding. When the caul has been removed from the: base plate, the caul pieces are readily, disassociated from each other and the hammer molding.

The. foregoing description sets forth the moth-- d. of applying an under-felt T0 to the hammer molding. If two felts are to be applied to the.

hammer molding, the top-felt 12 is glued to the under-felt. and the hammer molding in exactly the same manner as the under-felt is applied to the hammer molding.

In the accompanying drawings, particularly Figures 2 and 6, the mold cavity is shown for the purpose of applying a top-felt to an under-felt Ill and a hammer molding l8. After the top-felt has been applied to the hammer molding, and the felted molding has been removed from the mold clamp, the hammer molding and its associated felt is. cut into the proper number of individual hammers by cutting the felt on the hammer molding transversely of its length at the. proper intervals to form approximately ninetyfiv-e individual hammers. Eighty-eight hammers are needed for a standard piano, thirty-two hammers for the bass section of the piano, and fiftysiX hammers for the treble section of the piano,

the extra hammers being provided as spares,

available for replacement of any hammers that may become damaged or broken while being assembled in a. piano.

As previously stated, prior mold. clamps could not be relied upon to produce satisfactory piano hammers, since the basev plate of the. mold clamp was subjected to bowing and twisting, which resulted in movement of the clamping plates, and consequently, unsatisfactory application of'pressure to. the feltand to the hammer molding. This release of pressure on the hammer molding resulted in the unsatisfactory gluing and conse quently the necessity for repairing orrejecting certain of the. separate hammers of each set formed, or the. repair or rejection of the entire set of hammers formed, by each mold clamp.

The, present. invention obviates the need for wedging the caul into the groove of the base plate.. The doing away with the wedging action relieves to a substantial extent, the pressures and stresses to'which the base plate was previously subjected. In addition, the provision of end plates or bridges at the ends of the groove in the base plate, which Walls or bridges were heretofore iIXlpossible, so strengthens the base plate. as to resist any tendency to bow or twist. Consequently, the base plate retains its original shape and the clamping plates are retained and locked in the position to which they are moved by tllepressing members of the press. Consequently, each mold exerts the proper amount of pressure upon the felt in the hammer mold therein and does not allow the expansive force exerted by the felt to disturb. or vary the adjustment or relative positioning of the clamping plates and the'base plate. This results in the proper and complete gluing of the felt to the hammer molding throughout the entire length and over the entire surface area of the hammer molding. Therefore, theonly repairs or rejections of hamrner moldings. or separate hammers when formed with the clamp of the present invention would be the result of carelessness on the part of the Workman tightening the nuts to lock the clamping plates'to thebase pl e, d such reject o s could be traced directly to an individual, rather than to any fault in the machinery or apparatus utilized in forming the felted hammer moldings.

It. will be understood that in apparatus and equipment of this nature, certain changes, modifications, and other arrangements may be made without departing from the principles and scope of the: invention. Accordingly, all matter described above or shown in the accompanying drawings is intended to be interpreted as illustrative and not in a limited sense, the invention being defined by the appended claim.-

I claim:

In a gluing clamp for securing felts to piano hammer moldings, a base plate having at its under face a lengthwise rib of substantial width and uniform cross section provided with an upwardlyopeninglengthwise groove for reception. of'a caul, said groove being of uniform cross section throughout its caul receiving area and closed at its ends by bridging elements of substantial thickness lengthwise of said groove and integral with said: plate and rib, and opposed clamp plates adjustably mounted on said base plate at. opposite sides of said; groove.

SAMUEL E. ZACK.

References Cited in the file of this patent UNITED STATES. PATENTS Number. 

